1. Field of the Invention
The present invention relates to a monomorph type piezoelectric/electrostrictive device and a method for manufacturing the same.
2. Description of the Related Art
Heretofore, piezoelectric/electrostrictive devices have been known as elements capable of controlling a micro displacement of the order of submicrons. In particular, piezoelectric/electrostrictive devices, in which a piezoelectric/electrostrictive portion composed of a piezoelectric/electrostrictive ceramic composition (hereafter may simply be referred to as “piezoelectric ceramic”) and electrode portions to be applied with a voltage are laminated on a ceramic substrate, are suitable for controlling a micro displacement and, in addition, have excellent characteristics, for example, a high electromechanical conversion efficiency, high-speed responsivity, high durability, lower power consumption. These piezoelectric/electrostrictive devices are used in various applications, for example, piezoelectric pressure sensors, probe drive mechanisms of scanning tunneling microscopes, rectilinear guide mechanisms of ultraprecision machining apparatuses, hydraulic control servo valves, video tape recorder heads, pixels in flat-panel image display apparatuses, ink-jet printer heads, and the like.
Various studies have also been conducted on the piezoelectric ceramic constituting the piezoelectric/electrostrictive portion. For example, in recent years, there is a tendency to perceive influences exerted on the global environment, such as, elution of lead (Pb) by an acid rain, as problems. Therefore, (Li,Na,K) (Nb,Ta)O3 based piezoelectric ceramic capable of providing a piezoelectric/electrostrictive body or a piezoelectric/electrostrictive device, which exhibit satisfactory piezoelectric/electrostrictive characteristics even when lead (Pb) is not contained, has been developed as a piezoelectric/electrostrictive material in consideration of the influence exerted on the environment.
Since the piezoelectric ceramic is a ferroelectric substance, a polarization treatment must be conducted in order to take advantage of the properties (piezoelectric characteristics) by incorporating the piezoelectric ceramic into an electronic device or the like. This polarization treatment refers to a treatment of aligning the direction of the spontaneous polarization in a specific direction by applying a high voltage, and the treatment is conducted by, for example, applying a voltage to the piezoelectric ceramic under an appropriate temperature condition. That is, a plurality of domains are present in the ferroelectric substance due to uneven distribution of electric charges by the spontaneous polarization, and the piezoelectric ceramic is subjected to the polarization treatment of aligning the direction of domains of ferroelectric substance in a predetermined direction.
Some piezoelectric/electrostrictive devices made of the piezoelectric ceramic have a force of constraint oil one surface by being joined with a different type of material such as a metal plate. In such a piezoelectric/electrostrictive device, cracks are generated in a sintered body during firing for being joined to the different type of material, due to the difference in thermal expansion coefficient between the piezoelectric material and the metal plate. Furthermore, the temperature is increased by heat generation of the piezoelectric ceramic during use, and cracking occurs due to difference in thermal expansion coefficient between the piezoelectric material and the metal plate, therefore the characteristics deteriorate.
There is disclosed a monomorph type actuator in which the composition in the thickness direction is changed continuously so as to become a gradient material exhibiting continuously varying characteristics (See JP-A-4-239187).
However, several types of powders having different compositions must be prepared in order to produce a compositionally gradient material and, thereby, the production costs tend to be increased.